In the related art, there is known a device which conveys a conveyance object within a casing (see, e.g., Patent Document 1). The device disclosed in Patent Document 1, which is a device that conveys a workpiece such as a semiconductor wafer or the like, includes an accommodating box, a conveyance chamber, a load lock and a processing chamber. A semiconductor wafer accommodated within the accommodating box is carried out by a conveyance unit disposed within the conveyance chamber, and carried into the load lock to be subjected to specified processing within the processing chamber. The semiconductor wafer thus processed is carried out from the load lock by the conveyance unit, and carried into the accommodating box or conveyed to a load lock connected to another processing chamber. A blowing fan that generates airflow (a down-flow) from an upper side toward a lower side of the conveyance chamber and a filter are located in an upper area within the conveyance chamber. A ventilation outlet is provided in a bottom portion of the conveyance chamber. The conveyance chamber is configured such that clean gas is circulated by the blowing fan and the ventilation outlet.